1. Field of the Invention
This invention relates to identification badges. In one aspect the invention relates to time-limited or temporary identification badges while in another aspect, the invention relates to self-expiring identification badges. In yet another aspect, the invention relates to a method of making a self-expiring identification badge.
2. Description of the Related Art
In the field of building security, the need for recognition of authorized personnel is significant. For employees and others who are regularly in secure areas, this is accomplished with identification (ID) badges, preferably photographic ID badges.
For workers and visitors to secure areas who are short term guests, the self-expiring badge is typically used. This type of badge typically comprises two components. One component is an opaque layer which may have additional text or graphics imprinted on it. The other component includes a dye on its surface. When the dye is attached (usually by hand lamination) to the back side of the opaque layer, it is solubilized by an adhesive or plasticizer and then migrates through the opaque layer over time and appears on the front surface. Its appearance indicates expiration. This type of badge is exemplified by the two piece TEMPBADGE, manufactured and sold by Brady Corporation. Other examples are found in many patents including U.S. Pat. No. 4,903,254.
Attempts at making this more convenient for the end user have centered on reducing the design to one piece with a number of elements contained in it. The components of the one piece are then rearranged by folding and/or removing protective liners to accomplish the lamination needed to activate the badge and initiate the timing process. See, for example, U.S. Pat. Nos. 7,742,366 and 7,215,604.
In the field of user printed badges, common and convenient methods include the use of direct thermal and thermal transfer printers. Direct thermal printers work with common media that employ dye chemistry for thermally imaging. This chemistry usually utilizes a leuco-dye along with a dye developer. The dye developer is typically an acid that is inactive at room temperature, but is activated by heat, sometimes by melting and sometimes by being solubilized by an accelerator that melts. The acid then reacts with the leuco-dye to form an image. Examples of this technology are very widespread and find common use as receipt paper in every day transactions. As it is so widespread, the printing technology and the chemistry are conveniently available. The image formation is nearly instantaneous when exposed to the heat supplied by the thermal printer.
Another approach to time expiration indication is the solubilization of an organic acid in a pressure-sensitive adhesive (PSA). This adhesive is coated on a clear film and supplied to the end-user as an over-laminate. In this case to activate the timing, the end-user must place the over-laminate on top of a direct thermal paper. The rate of migration of the organic acid from the adhesive determines the rate of image development and expiration indication (see, for example, U.S. Pat. No. 6,544,925). The requirement for end-user action in the initiation step, however, is still somewhat complicated.
Although a thermal transfer printer works using a similar heating process, the image is formed by the transfer of ink from a ribbon to a media. The ribbon comprises ink coated on a thin, heat resistant substrate (such as polyester film). Typically these are formulated using a pigment such as carbon black that is dispersed in a polymer binder. When heated, the binder will adhere to a substrate and transfer from the ribbon. Various binders as well as substrates and top coatings are employed for this purpose to achieve specialized performance.
All of these methods require active end-user participation which is both inconvenient and offers greater chance for defeating the timing mechanism (such as forgetting or refusing to activate the badge). As such there is an ongoing need for an improved method that will conveniently initiate a self-expiring badge on demand by the end-user.